Materials closely resembling vertebrate-type peptide hormones (insulin, somatostatin, adrenal-corticotrophin hormone, relaxin, calcitonin, arginine-vasotocin) have been identified in unicellular organisms. These studies were extended to include a search for similar peptides in plants. Insulin and somatostatin-related materials were found in extracts of spinach, lemna and rye. Purification of the peptides was achieved using gel chromatography and high performance liquid chromatography and activity demonstrated by the specific hormone radioimmunoassays and bioassays. Using recombinant DNA technology, the genes encoding for insulin and somatostatin were searched for in genomic extracts from unicellular eukaryotes and prokaryotes as well as Drosophila. Specific DNA sequences were found which hybridized to cDNA probes for rat somatostatin and rat insulin and are currently being analyzed for sequence composition. Clones with lambda gt11 expression were probed with anti-insulin and anti-somatostatin antibodies. Positive clones are being processed for nucleotide sequences. These results suggest that hormone-like peptides are evolutionarily very old.